AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
The nucleophilic addition–elimination reactions of ammonia and primary…
Full specification wording
Nucleophilic properties (A-level only): The nucleophilic addition–elimination reactions of ammonia and primary amines with acyl chlorides and acid anhydrides.
Ammonia and primary amines attack the carbonyl carbon of an acyl chloride or an anhydride, and the chloride or carboxylate is then eliminated, so the product keeps the C=O and gains a nitrogen.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 4 of 5
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Ammonia and primary amines attack the carbonyl carbon of an acyl chloride or an anhydride, and the chloride or carboxylate is then eliminated, so the product keeps the C=O and gains a nitrogen. Ammonia with ethanoyl chloride gives ethanamide, CH₃CONH₂; a primary amine such as methylamine gives the N-substituted amide CH₃CONHCH₃. The inorganic product is hydrogen chloride, but it never survives free: a second mole of ammonia or amine takes it up as the ammonium or alkylammonium salt, so two moles of the nitrogen compound are used per mole of acyl chloride, and a white smoke of the solid salt is seen. Ethanoic anhydride gives the same amide but releases ethanoic acid instead, and reacts less violently.
What earns the marks
- The amide drawn with the nitrogen bonded directly to the carbonyl carbon.
- The N-substituted amide when a primary amine is used in place of ammonia.
- Two moles of ammonia or amine per mole of acyl chloride.
- Ethanoic acid rather than hydrogen chloride as the second product with an anhydride.
Common mistakes and how to put them right
Giving an amine salt rather than the amide as the organic product.
Writing the equation with one mole of ammonia and free hydrogen chloride alongside the amide.
Writing HCl as a product when the reagent given was ethanoic anhydride.
Naming CH₃CONHCH₃ as an amine because it contains an N-H bond.
Exam tips
- Check the mole ratio before you balance: if the nitrogen compound is also a base, you need a second mole of it.
- An amide has the nitrogen on the carbonyl carbon; an amine has it on a saturated carbon. Look at what the nitrogen is bonded to before you name the product.
Try the lesson
The start of the Nucleophilic properties (A-level only): The nucleophilic addition–elimination reactions of ammonia and primary amines with acyl chlorides and acid anhydrides. lesson, made from checked teaching notes for this specification point.
Have a go first
Which product is formed when ammonia reacts with ethanoyl chloride?
Listen
Ammonia and primary amines attack the carbonyl carbon of an acyl chloride or an anhydride, and the chloride or carboxylate is then eliminated, so the product keeps the C=O and gains a nitrogen. Ammonia with ethanoyl chloride gives ethanamide, CH₃CONH₂; a primary amine such as methylamine gives the N-substituted amide CH₃CONHCH₃. The inorganic product is hydrogen chloride, but it never survives free: a second mole of ammonia or amine takes it up as the ammonium or alkylammonium salt, so two moles of the nitrogen compound are used per mole of acyl chloride, and a white smoke of the solid salt is seen. Ethanoic anhydride gives the same amide but releases ethanoic acid instead, and reacts less violently. A strong answer earns marks for these points. the amide drawn with the nitrogen bonded directly to the carbonyl carbon. the N-substituted amide when a primary amine is used in place of ammonia. two moles of ammonia or amine per mole of acyl chloride. ethanoic acid rather than hydrogen chloride as the second product with an anhydride. Exam tip: Check the mole ratio before you balance: if the nitrogen compound is also a base, you need a second mole of it.
Key words
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amide formation
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anhydride versus acyl chloride
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See every definition
- amide formation
- Ammonia or a primary amine attacks the carbonyl carbon of an acyl chloride or an anhydride, and the chloride or carboxylate is eliminated, so the product keeps the C=O and gains a nitrogen.
- anhydride versus acyl chloride
- Ethanoic anhydride gives the same amide but releases ethanoic acid instead of hydrogen chloride, and reacts less violently.
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